1. Field of the Invention
The present invention relates generally to a ball screw and more particularly, to a ball screw capable of sensing a preload.
2. Description of the Related Art
The ball screw is a common component for precision positioning and includes a screw for rotation driven by a motor, a nut for linear movement driven by the screw, and a plurality of balls mounted between the screw and nut. Rolling of the balls serves as the power transfer interface between the screw and nut to greatly reduce the frictional resistance generated while the balls roll.
The ball screw is usually provided with preload inside itself for eliminating axial clearance among the balls, the screw, and the nut to further increase the rigidity, positioning precision, and positioning stability of the running ball screw, so the preload is one of significant indexes of measuring the rigidity, positioning precision, and positioning stability of the running ball screw. However, after the ball screw is used for a while, wear and tear among the screw, the nut, and the balls leads to axial clearance to make the preload disappear gradually, so the rigidity, positioning precision, and positioning stability of the ball screw become decreasing.
Taiwan Patent Laid-open No. 201204960 disclosed a method diagnostic of preload ineffectiveness of a ball screw and a device based on the method, in which a voiceprint signal generated while the ball screw is working can be filtered by empirical mode decomposition (EMD), then processed by Hilbert-Huang transform (HHT) to generate Hilbert-Huang spectrum (HHS), next processed by multi-scale entropy extraction to generate multi-scale entropy complexity mode, and after the raw multi-scale entropy complexity mode and the current multi-scale entropy complexity mode are compared, whether a preload of the ball screw disappears or not can be effectively diagnosed. However, in the process of measurement based on this method, the measurement is not applied straight to how the ball screw is forced and the measuring accuracy is adversely affected very easily subject to other environmental factors, such as vibration, noise, or frequency generated during the processing, so it still fails to provide accurate measuring outcome.